mgaido91 commented on a change in pull request #25029: [SPARK-28228][SQL] Fix substitution order of nested WITH clauses URL: https://github.com/apache/spark/pull/25029#discussion_r302704485
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CTESubstitution.scala ########## @@ -0,0 +1,132 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.spark.sql.catalyst.analysis + +import org.apache.spark.sql.catalyst.expressions.SubqueryExpression +import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, With} +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.internal.SQLConf + +/** + * Analyze WITH nodes and substitute child plan with CTE definitions. + */ +object CTESubstitution extends Rule[LogicalPlan] { + def apply(plan: LogicalPlan): LogicalPlan = if (SQLConf.get.legacyCTESubstitutionEnabled) { + legacyTraverseAndSubstituteCTE(plan) + } else { + traverseAndSubstituteCTE(plan, false) + } + + private def legacyTraverseAndSubstituteCTE(plan: LogicalPlan): LogicalPlan = { + plan.resolveOperatorsUp { + case With(child, relations) => + // substitute CTE expressions right-to-left to resolve references to previous CTEs: + // with a as (select * from t), b as (select * from a) select * from b + relations.foldRight(child) { + case ((cteName, ctePlan), currentPlan) => substituteCTE(currentPlan, cteName, ctePlan) + } + } + } + + /** + * Traverse the plan and expression nodes as a tree and replace matching references to CTE + * definitions. + * - If the rule encounters a WITH node then it substitutes the child of the node with CTE + * definitions of the node right-to-left order as a definition can reference to a previous + * one. + * For example the following query is valid: + * WITH + * t AS (SELECT 1), + * t2 AS (SELECT * FROM t) + * SELECT * FROM t2 + * - If a CTE definition contains an inner WITH node then substitution of inner should take + * precedence because it can shadow an outer CTE definition. + * For example the following query should return 2: + * WITH + * t AS (SELECT 1), + * t2 AS ( + * WITH t AS (SELECT 2) + * SELECT * FROM t + * ) + * SELECT * FROM t2 + * - If a CTE definition contains a subquery that contains an inner WITH node then substitution + * of inner should take precedence because it can shadow an outer CTE definition. + * For example the following query should return 2: + * WITH t AS (SELECT 1 AS c) + * SELECT max(c) FROM ( + * WITH t AS (SELECT 2 AS c) + * SELECT * FROM t + * ) + * - If a CTE definition contains a subquery expression that contains an inner WITH node then + * substitution of inner should take precedence because it can shadow an outer CTE + * definition. + * For example the following query should return 2: + * WITH t AS (SELECT 1) + * SELECT ( + * WITH t AS (SELECT 2) + * SELECT * FROM t + * ) + * @param plan the plan to be traversed + * @param inTraverse whether the current traverse is called from another traverse, only in this + * case name collision can occur + * @return the plan where CTE substitution is applied + */ + private def traverseAndSubstituteCTE(plan: LogicalPlan, inTraverse: Boolean): LogicalPlan = { + plan.resolveOperatorsUp { + case With(child: LogicalPlan, relations) => + // child might contain an inner CTE that has priority so traverse and substitute inner CTEs + // in child first + val traversedChild: LogicalPlan = child transformExpressions { + case e: SubqueryExpression => e.withNewPlan(traverseAndSubstituteCTE(e.plan, true)) + } + + // Substitute CTE definitions from last to first as a CTE definition can reference a + // previous one + relations.foldRight(traversedChild) { + case ((cteName, ctePlan), currentPlan) => + // A CTE definition might contain an inner CTE that has priority so traverse and + // substitute ctePlan Review comment: nit: ```suggestion // substitute CTE defined in ctePlan. ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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